Location systems for locating objects or personnel within a facility are known. One type of personnel location system used in hospitals involves personnel within the facility reporting their locations by manually setting switches at designated areas. The switches are monitored at a central station and the locations of the personnel are determined by the locations of the activated switches. Other proposed personnel or object location techniques include systems which locate personnel or objects by seeking out where the object or personnel is closest to designated monitors. Such systems generally include a central controller connected to a plurality of transceivers distributed at designated locations throughout a facility. Portable units are worn or attached to objects or personnel to be located. Each portable unit is assigned a unique identification. To locate a personnel, the central controller causes the transceivers to broadcast or page the portable unit by its identification. The broadcast or page signal is received by the portable units but only the portable unit having a matching identification will respond with a confirmation signal, which is received by the transceiver located closest to the responding portable unit. The transceiver in turn reports to the central controller that it has received a confirmation signal. The location of the portable unit is determined by the central controller by the message received from the transceiver. Location systems employing such location technique are described in U.S. Pat. No. 4,649,385 to Aires et al. and U.S. Pat. Nos. 3,805,265, 3,805,226 and 3,696,384 to Lester. One problem with the systems of this type is in the portable units. They must include electronics with adequate sensitivity to receive signals broadcast from the transceivers and adequate power to transmit a reply. The portable units became bulky and cumbersome and therefore inconvenient to be worn or attached.
U.S. Pat. No. 4,955,000 to Nastrom and U.S. Pat. No. 5,119,104 to Heller propose location reporting systems which include portable electronic units worn or attached to objects. The portable units periodically transmit individually unique ID signals. A plurality of transceivers are distributed at designated locations and the transceiver(s) within range of the portable unit transmissions receives the transmitted ID signals. The transceiver(s) in turn communicates the ID information to the central control unit. From the location of the transceiver and the ID of the portable unit, the central control unit is able to determine the location of the object. A disadvantage of this type of location system is the large amount of energy required to periodically transmit information from a portable unit, causing a continual drain on the power source. A large battery is required for usage of the portable unit for any meaningful period of time. The size of the portable unit is then dictated by the size of the battery. Further, unless the portable unit is efficiently used, frequent battery replacement and maintenance is required.
It can be seen that there exists a need for a location system having portable units which are compact in size and include capability to optimize the efficiency of operation.